Latent Task Embedding: Geometric Expansion for Single-Path Multi-Task PEFT

Junhyun Lee, Seoha Song, Dhananjaya Gowda


Abstract
Parameter-efficient fine-tuning (PEFT) typically relies on additive weight perturbation. However, in dynamic deployment environments like multi-tenant cloud serving or mobile edge devices, additive methods force a dilemma: merge weights and lose task-switching flexibility, or remain unmerged and suffer severe parallel-branching latency. To break this bottleneck, we propose Latent Task Embedding (LatTE), which shifts the PEFT design axis to geometric expansion. Instead of perturbing frozen parameters, LatTE concatenates a task-specific auxiliary embedding to the input and expands the corresponding weight matrices. This structural fusion ensures the forward pass remains a single, optimized matrix multiplication, bypassing the routing overhead of unmerged adapters. Furthermore, LatTE natively supports router-free, intra-batch multi-tasking by isolating tasks into distinct subspaces controlled via binary masking. Extensive evaluations across 1B to 14B parameter models demonstrate that LatTE matches highly optimized baselines like LoRA, while raising throughput by 1.7× over routed multi-adapter LoRA under heterogeneous-task batching.
Anthology ID:
2026.emnlp-main.2649
Volume:
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
EMNLP
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
60275–60293
Language:
URL:
https://aclanthology.org/2026.emnlp-main.2649/
DOI:
Bibkey:
Cite (ACL):
Junhyun Lee, Seoha Song, and Dhananjaya Gowda. 2026. Latent Task Embedding: Geometric Expansion for Single-Path Multi-Task PEFT. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 60275–60293, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Latent Task Embedding: Geometric Expansion for Single-Path Multi-Task PEFT (Lee et al., EMNLP 2026)
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PDF:
https://aclanthology.org/2026.emnlp-main.2649.pdf